Marcelo A. Villar

Thermoplastic starch films reinforced with talc nanoparticles

Nanocomposite films of thermoplastic corn starch (TPS) with talc particles were obtained by thermo-compression in order to study the effect of filler on structure, optical, and thermal properties. Talc increased the films rigid phase, thus their cross-sections resulted more irregular. Talc preferential orientation within matrix and good compatibility between particles and TPS was observed by SEM. Slight crystalline structure changes in TPS matrix were measured by XRD and DSC, due to talc nucleating effect. Randomly dispersed talc nanoagglomerates and individual platelets were assessed by TEM. Laminar morphology and nano-sized particles allowed that nanocomposite films were optically transparent. TPS-talc films resulted heterogeneous materials, presenting domains rich in glycerol and others rich in starch. Talc incorporation higher than 3%, w/w increased softening resistance of the nanocomposites as stated by DMA. Relaxation temperatures of glycerol-rich phase shifted to higher values since talc reduces the mobility of starch chains.

Influence of the extraction–purification conditions on final properties of alginates obtained from brown algae (Macrocystis pyrifera)

In this work, three methods (ethanol, HCl, and CaCl(2) routes) of sodium alginate extraction-purification from brown seaweeds (Macrocystis pyrifera) were used in order to study the influence of process conditions on final properties of the polymer. In the CaCl(2) route, was found that the precipitation step in presence of calcium ions followed by proton-exchange in acid medium clearly gives alginates with the lowest molecular weight and poor mechanical properties. It is well known that the acid treatment degrade the ether bonds on the polymeric chain. Ethanol route displayed the best performance, where the highest yield and rheological properties were attained with the lowest number of steps. Although the polymer I.1 showed a molar mass and polydispersity index (M(w)/M(n)) similar to those of commercial sample, its mechanical properties were lower. This performance is related to the higher content of guluronic acid in the commercial alginate, which promotes a more successful calcium chelation. Moreover, the employment of pH 4 in the acid pre-treatment improved the yield of the ethanol route, avoiding the ether linkage hydrolysis. Therefore, samples I.2 and I.3 displayed a higher M(w) and a narrower distribution of molecular weights than commercial sample, which gave a higher viscosity and better viscoelastic properties.

Evaluation of by-products from the biodiesel industry as fermentation feedstock for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production by Cupriavidus necator

Utilization of by-products from oilseed-based biodiesel production (crude glycerol, rapeseed meal hydrolysates) for microbial polyhydroxyalkanoate (PHA) production could lead to the replacement of expensive carbon sources, nutrient supplements and precursors for co-polymer production. Batch fermentations in shake flasks with varying amounts of free amino nitrogen led to the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) with a 2.8-8% 3HV content. Fed-batch fermentations in shake flasks led to the production of 10.9g/L P(3HB-co-3HV) and a 55.6% P(3HB-co-3HV) content. NaCl concentrations between 2 and 6g/L gradually became inhibitory to bacterial growth and PHA formation, whereas in the case of K(2)SO(4), the inhibitory effect was observed only at concentrations higher than 20g/L. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and nuclear magnetic resonance ((13)C NMR) demonstrated that the incorporation of 3HV into the obtained P(3HB-co-3HV) lowered glass transition temperature, crystallinity and melting point as compared to polyhydroxybutyrate. Integrating PHA production in existing oilseed-based biodiesel plants could enhance the viability and sustainability of this first generation biorefinery.

Rheological properties of thermoplastic starch and starch/poly (ethylene-co-vinyl alcohol) blends

Abstract Blends consisting of a systematic compositional series of starch/poly(ethylene-co-vinyl alcohol) were studied by using capillary viscometry. Three different types of starches were used: waxy maize, a starch containing essentially 100% amylopectin; native corn, possessing approximately 70% amylopectin and 30% amylose; and a treated, high-amylose starch, consisting of approximately 30% amylopectin and 70% amylose. Poly(ethylene-co-vinyl alcohol) with 44 mol% ethylene was blended in varying proportions with the starches, and glycerine and water were added as plasticizers. The viscosity of the blends was measured over the shear-rate range 1–1000 s−1. Samples unconditioned (as stored) as well as conditioned at 65% relative humidity and 23°C were measured at temperatures between 140 and 170°C. All viscosity results fall in the power-law regime, and there is no indication of approach to a zero-shear-rate viscosity in any of the starch blend systems. As in starch-based food materials, the viscosity has an Arrhenius dependence on temperature, an exponential dependence on moisture content and a power-law dependence on shear rate. The power-law exponents from the starch blends are less than unity, indicating that the melts are shear thinning. Results on the starch/poly(ethylene-co-vinyl alcohol) blends indicate that the viscosity decreases with decreasing amylose content or increasing poly(ethylene-co-vinyl alcohol) content. The shear-rate dependence increases with an increase in the amylose content of the blends.

Biosynthesis of PHB from a new isolated Bacillus megaterium strain: Outlook on future developments with endospore forming bacteria

Diverse Bacillus strains are known as producers of polyhydroxyalkanoates (PHAs) under nutrient-limiting conditions. However, these limiting conditions have the same nutritional characteristics that stimulate spore generation in Gram-positive microorganisms. In the present work, a new isolated Bacillus megaterium strain was characterized based on 16S rRNA gene sequences (1,411 bp) and studied in terms of its ability for producing polyhydroxybutyrate (PHB) by implementing different fermentation configurations on formulated media. The isolated strain was able to produce PHB up to 59 and 60% of its dry cell weight during bioreactor experiments employing glucose and glycerol as carbon source, respectively. The produced biopolymer was characterized and identified by using carbon-13 nuclear magnetic resonance (13C-NMR) and Fourier transform infrared (FTIR) techniques. In spite of the sporulation phenomenon existing in Bacillus strains, obtained results demonstrate that the new isolated strain has the potential of accumulating high levels of intracellular PHB. Supported by these experimental results and by those reported by other authors, the last section of this paper gives an outlook of future research topics on PHB and polyhydroxyalkanoate (PHA) copolymers production by Gram-positive bacteria. The importance of combining bioprocessing/biorefinering concepts with bioreactor optimization approaches is stressed and analyzed based on current PHAs research trends.

Co‐ and terpolymerization of ethylene, propylene, and higher α‐olefins with high propylene contents using metallocene catalysts

The copolymerization of propylene/ethylene and terpolymerization of propylene/ethylene/α-olefins using long-chain α-olefins such as 1-octene and 1-decene have been carried out using EtInd2ZrCl2//methylaluminoxane. High concentrations of propylene and low concentrations of α-olefins (near 2 mol % of the total olefin concentration in the liquid phase) were used. The effect of the ethylene concentration in copolymerizations of propylene/α-olefins was studied at medium ethylene contents (12 and 40 mol % in the gas phase). The polymers were molecularly characterized by gel permeation chromatography-multiangle laser light scattering, wide-angle X-ray scattering, Fourier transform infrared spectroscopy, and DSC analyses. The shorter α-olefin studied (1-octene) produced the highest improvement of activity in terpolymerization at 12 mol % ethylene in the gas phase. About 2 mol % of 1-octene in the liquid phase increases the activity and decreases the molecular weight of terpolymers with respect to corresponding copolymers, whereas the mp is increased by almost 30 °C. The “termonomer effect” is less evident when higher amounts of ethylene are used.

Influence of polydispersity on the viscoelastic properties of linear polydimethylsiloxanes and their binary blends

Abstract Linear polydimethylsiloxanes of relatively narrow molecular weight distribution (MWD) were synthesized by anionic polymerization and characterized by different techniques. Binary blends were also prepared with some of the synthesized polymers. Linear viscoelastic parameters, such as storage (G′) and loss (G″) moduli, were obtained at different temperatures as functions of frequency (ω). The time–temperature superposition principle was applied in order to increase the frequency range measured. Zero-shear rate viscosity (η0), steady-state recoverable compliance (Je0) and zero-shear rate first normal stress coefficient (ψ1,0) were calculated from the data corresponding to the terminal relaxation zone. The molecular weight dependence of those parameters shows a good agreement with classical models and previously reported results, although Je0 and ψ1,0 are strongly affected by polydispersity. Different polydispersity factors were applied in order to fit the experimental values of the viscoelastic properties with the theory.

Permeability and diffusional studies on silicone polymer networks with controlled dangling chains

The permeability to oxygen of silicone polymer networks with controlled high-molecular-weight side chains was measured using electrochemical techniques. Networks with controlled amounts of pendent chains were prepared by hydrosilation reactions involving the addition of hydrosilanes from crosslinking molecules to the vinyl end-groups of mono- and difunctional prepolymer molecules. Values of the permeability coefficient P were determined by measuring the steady electric current in an experimental set-up in which several layers of moistened paper were placed between the network and the electrodes. The curve representing the dependence of the permeability coefficient on the molecular weight of the dangling chains, M, shows that, for values of M 130 000, the permeability coefficient does not show a noticeable dependence on the molecular weight of the dangling chains. The diffusion coefficient increases with the molecular weight of the side chains, reaching a nearly asymptotic value for M ≈ 170 000.

Thermogravimetric analysis of starch-based biodegradable blends

SummaryThermogravimetric analysis (TGA) has been shown to be a useful technique to determine the content of starch and other components that are usually present in blends of starch with synthetic polymers. However, some of these blends are composed of elements with an important superposition in their temperature degradation range. In these cases interpretation of the TGA results becomes quite difficult and usually important errors are committed in the determination of blend composition. We present here a method to improve the accuracy of the interpretation of TGA data. The analysis was developed to study blends containing starch, an ethylene-vinyl alcohol copolymer, and water plus glycerin as plasticizers. Using this procedure it is possible to predict blend composition with an error less than 3%, even when there is an appreciable superposition between the temperature degradation range of starch and poly(ethylene-co-vinyl alcohol). As the proposed method of analysis is quite general it may be extended to be used with other types of blends that give thermograms with similar characteristics to those described in this paper.

Irradiation‐modification of starch‐containing thermoplastic blends. I. Modification of properties and microstructure

Irradiation-modification of the blends of various starches with a synthetic polymer [poly(ethylene-co-vinyl alcohol)] was carried out using an electron beam. The effect of irradiation on neat starches was studies using gel permeation chromatography. Changes in the thermal and mechanical properties of the blends, as well as in their microstructures, were also evaluated. The data indicate, consistent with other reports in literature, that starch molecules fragment under the effect of ionizing radiation, while the EVOH is relatively unaffected. These substantial (mainly physical) modifications to the starch molecules manifest themselves in changes in the thermal behavior of the blends. Furthermore, the mechanical properties of filaments obtained from molten irradiated pellets were quite different from those of control filaments, at least for some starches. Micrographic examination of some blends indicated a correspondence between a modification in the microstructure of the filaments and a change in their mechanical properties. It seems likely that the enhanced mobility of the fragmented starch molecules in the melt is responsible for these changes in the microstructure and concomitantly, the mechanical properties of the blend. Such an irradiation-based physical modification of starch may be of use in tailoring the properties of commercial blends of starches with synthetic thermoplastics.